The present invention relates to a choke valve for controlling pressurized fluid flow through a line, such as the flow produced by an oil or gas well. More particularly the invention relates to modifying the outlet of the valve and its flow trim cage to thereby reduce erosion of the valve body immediately downstream of the cage.
A choke valve (hereinafter referred to as a xe2x80x98chokexe2x80x99) is a throttling device. It is used to control flow rate while reducing the fluid pressure of a stream moving through a flow line. Chokes are commonly used in oil or gas drilling and production systems to provide throttling and shut-off with respect to high pressure streams.
The present invention was developed in connection with seeking to ameliorate the erosive effect of such streams when carrying abrasive solid particles, such as entrained sand.
A choke, previously developed by the assignee of this application, is disclosed in U.S. Pat. No. 6,105,614. This choke is illustrated in FIG. 1 of this specification. In general, the choke comprises:
a valve body a having a T-shaped bore structure consisting of an inlet bore b, an outlet bore c and a component bore d;
the choke internals are positioned in the component bore d, which communicates with the inlet and outlet bores b, c. The internals comprise a flow trim e, having a tubular cylindrical cage f, whose side wall g forms ports h, and a tubular cylindrical sleeve i for sliding along the cage f, together with means j for advancing or retracting the sleeve and suitable sealing means k.
In the operation of the choke, the flow stream moves through an L-shaped passageway formed by the body inlet bore b, the cage ports h, the cage bore 1, and the body outlet bore c. The sleeve i functions to throttle flow by adjusting the area of the ports h.
It will be noted that the valve body outlet bore c has a reduced diameter section m, an expanding diameter transition section n and a full diameter section o which corresponds with the internal diameter of the downstream flow line (not shown).
In the course of passing through the choke, the velocity of the stream increases. This occurs because the passageway cross-sectional areas in the choke are smaller than the bore cross-sectional area of the flow lines upstream and downstream of the choke. This acceleration exacerbates erosive effects on the choke.
The valve body of the choke typically is made of relatively softer steel, to permit the body to be machined. In contrast, the flow trim is made of harder material, to better resist erosion as the stream makes a right angle turn through the flow trim.
Our inspection of used chokes has shown that severe erosion of the valve body commonly occurs along the reduced diameter section m of the valve outlet bore c, immediately downstream of the cage f.
It is the objective of the present invention to improve the choke""s ability to withstand erosion downstream of the flow trim.
As a result of experimental work involving test runs of pressurized fluid through a choke, we have discovered:
that provision of an annular, inwardly protruding lip at the outlet of the cage bore will deflect the fluid flow inwardly so as to reduce erosion of the valve body along the reduced diameter section of the outlet bore; and
that preferred conditions in this connection are:
(1) that the lip should protrude inwardly less than about 0.060 inches relative to the surface of the valve body outlet bore reduced diameter section;
(2) that the transition section of the valve body outlet bore should be spaced at least 0.5 inches and less than 1.125 inches from the cage bore outlet;
(3) that the lip should be formed as an inclined ramp having an inclination of about 10xc2x0; and
(4) the transition angle between the reduced diameter section of the outlet bore and the full diameter section should be in the range of 25xc2x0-35xc2x0. [To match the fluid re-entry angle thereby reducing erosion to the transition area between bore m and bore o.]
If any of these limitations are not met, then there is a tendency to create eddy currents at the valve body surface of the reduced diameter section of the outlet bore, with some consequent erosion.
Broadly stated, the invention is directed to a choke valve for controlling pressurized fluid flow in a line, comprising: a valve body forming an inlet bore, a component bore and an outlet bore; each bore having an inlet and an outlet; the component bore connecting the outlet of the inlet bore and the inlet of the outlet bore; a flow trim positioned in the component bore for controlling flow through the bores, said flow trim comprising a tubular cage having upstream and downstream ends, said cage having a side wall with an inner surface forming a longitudinal bore, said cage side wall forming flow ports extending therethrough at its upstream end, and a tubular sleeve operative to slide along the cage to throttle the ports; means, extending into the component bore, for biasing the sleeve along the cage; means for sealing the flow trim and biasing means within the component bore; the cage being formed of harder material than the body; the cage side wall forming an inwardly protruding lip at the downstream end of the cage bore for deflecting fluid passing through the valve toward the center of the valve body outlet bore to thereby reduce erosion of the valve body immediately downstream of the cage.